This invention relates generally to conveyor systems, and more particularly to conveyor systems having an endless conveying surface and diverter shoes mounted on the support members making up the conveying surface, for lateral movement with respect to the conveying surface. The invention is especially adapted to divert packages selectively to one or more sortation spurs extending laterally from the conveying surface.
Article diverters using a moving conveying surface consisting of a plurality of parallel support members mounted to endless chains, have been known for a number of years. Such diverters utilize a diverter shoe movably mounted on each support member for lateral movement with respect to the conveying surface under the guidance of a track network. Diverting gates in the track network selectively transfer guidance of each diverter shoe from a track running in the direction of the movement of the conveying surface to a diagonal track in order to cause lateral movement of the diverter shoes In order to avoid wasted spacing between variable-length packages, such diverters may include manual or automatic measuring means at an infeed point to cause the diverter gate associated with the selected sortation spur to divert a selected number of shoes corresponding in general to the length of the package. Exemplary of this type of conveyor are U.S. Pat. No. 3,361,247, issued to James N. Lauzon et al and U.S. Pat. No. 4,738,347, issued to Brouwer, the latter being assigned to the present assignee.
While the use of the measured length of packages to select the number of shoes used to divert each package eliminates some wasted package spacing, the prior art requires that at least one diverter shoe be left unused between packages in order to avoid the diverting of one package from interfering with the diverting of a forward or trailing package Furthermore, the prior art diverters typically switch the selected number of diverter shoes onto a single diagonal track in order to laterally displace the package. Because the diverter shoes are aligned during the diverting motion in a diagonal across the moving conveying surface, the package is rotated with respect to the direction of movement The rotation of the packages increases their length in the direction of conveyor movement, which requires additional spacing between packages.
Another difficulty experienced with prior conveyor sortation systems is that a rapid series of diverts to a single spur may temporarily overload the accumulation section of the take-away conveyor for that particular spur. The powered accumulation section typically operates at a slower speed than the rest of the power-driven take-away conveyor. In order to avoid a jam-up, prior art systems monitor the back-up of packages in the accumulation section on the take-away conveyor associated with each spur and suspend diverts to that spur when a jam-up occurs This is traditionally accomplished by a photodetector, or other position sensor, with a suitable time delay to avoid actuation of the sensor by the momentary passage of a package along the conveyor, so that only an excess accumulation will be detected and only after it occurs. The required time delay creates a situation in which further accumulation may occur without detection, necessitating a conservative design approach, such as extra accumulation space, or by restricting the rate at which packages may be diverted, or both.